Tailoring the film morphology of para-hexaphenyl on KCl(001) by surface temperature

Abstract

Ultra-thin films of para-hexaphenyl (6P) were prepared on potassium chloride(001) utilising physical vapour deposition under well-defined ultra-high-vacuum conditions. The 6P growth characteristics were studied as a function of substrate temperature. For this purpose, in situ X-ray photoelectron spectroscopy (XPS) in combination with thermal desorption spectroscopy (TDS) was applied to reveal the kinetics of the layer growth. Ex situ atomic force microscopy (AFM) was used to determine the film morphology. At the initial growth stage the film grows in the form of needle-like islands with a high aspect ratio and, subsequently, when a certain coverage is reached, terraced mounds of 6P are formed. It is shown that this ‘certain coverage’ strongly depends on the substrate temperature and that the morphology of the film can be tailored easily by changing the surface temperature. Combined XPS and TDS investigations were carried out to obtain information on the stability of these films. It is shown that films grown at low temperature (90 K) rearrange during heating and this rearrangement could also be made visible by AFM.